Sure, the amp can be a cause of this - but I don't think it is in this case.
The source also matters, both the material and the DAC (Yggdrasil), both of which produce an incredibly vivd three dimensional sound stage with my speaker system, and a quite palpable one with either my Abyss or HD800S. Certainly the headphones here are no in the same realm as speakers for imaging, but they're still creating an image with both depth and width.
Power wise, the WA5LE has about 7 watts
into 200 ohms ... per the
manufacturer (I'm hedging between the values for 120 ohms and 300 ohms, so it might be closer to 8 watts or it might be closer to 6).
But regardless of all that, I think I know what's going on now after doing a little test that occurred to me on my drive home, and was verified with a couple of simple observations I asked my girlfriend to make:
It's the angle of the drivers in relation to my ears!
With the HD800S the pads are firm enough that they keep the drivers angled relative to my ears which allows the pinnae to have more of their natural effect, which is important for the psychoacoustics necessary for the brain to project a three dimensional sound-field
With the Abyss ... my preferred positioning has them also canted forward and since I run them with a very light seal (almost no seal), the frame keeps the driver's position constant. I know from how I wear the Abyss for different types of music that putting the drivers so they're parallel to my ears significantly reduces the soundstage.
With the LCD-4, and my largish head, the pads on the LCD-4 are compliant enough that the drivers wind up almost completely square-on to (parallel with) my ears. If I manually cant them forward a bit, then the soundstage suddenly develops quite a bit more depth and the width grows as well. It's still not as wide or deep an image as I get with the HD800S or Abyss (nor is it as wide as I recall the HE-1000 being) and it does me no real good knowing this since I can't keep the drivers in that position and actually listen to them, but it helps explain what is going on!
Different pads might change things ... but then they'd have other acoustic effects, so it is what it is. It's not something I've ever considered a
problem, just a
difference.